This invention relates to a burner system for burning wood-waste products, such as wood shavings, sawdust and wood chips.
Wood is one of the most important natural resources and one of the few that is renewable. Timber demand for all forest products is projected to rise faster than supplies from U.S. forests. It is increasingly important to utilize the wood harvest efficiently, use currently underutilized wood species and employ the considerable quantities of unused residues.
While wood and wood by-products are known for use as fuels, for a variety of reasons, natural gas, coal and oil have been preferred. Curtailment of supplies of these latter fuels, however, has created renewed interest in the use of wood and wood by-products as fuels for residential, commercial and industrial heating purposes. In addition, increasing concern about the damage caused by acid rain, which is believed to be based on the burning of high-sulphur coal and oil, makes wood and wood by-products even more attractive for use as fuels because wood is substantially free of sulphur.
Wood-waste combustion systems are known in the art, and they include pile burning and modified pile burning systems, such as Dutch ovens. Most of the wood and wood-waste products that are burned today are heterogenenous materials necessitating the use of a spreader-stoker or a pile-burning system. The modern spreader-stoker dominates; it is a water wall furnace with traveling grates, regenerative air heaters and extensive pollution control devices. The extensive fuel handling system required for wood-fired systems adds appreciably to the total cost of a combustion system.
Large amounts of fossil fuels are combusted in commercially available boilers, which are frequently referred to as "package boilers" because they are available in substantially ready-assembled form for installation at a plant site or other facility. Because package boilers have been in use for many years, numerous such devices are located throughout the country. However, most of the package boilers were designed to burn natural gas or fuel oil rather than a solid fuel, such as wood-waste.
In order to take advantage of the abundant supply of wood-waste materials as fuel in some parts of the country while avoiding the heavy capital investment required for a new solid fuel boiler, there exists a need for a wood-waste burner system that can be adapted to package boilers that were originally designed for burning natural gas or fuel oil. The wood-waste burner system should be of low cost relative to a new solid fuel boiler, it should be relatively easy to install in existing boiler facilities, require low maintenance, be simple to operate and above all provide efficient burning of the wood-waste products.